function returnBack(){

    header("Location:register.php");
    exit;

}

if(isset($_POST['myusername']))
{
    $myusername = $_POST['myusername'];
}
else
{
    returnBack();
}
if(isset($_POST['mypassword']))  {
    $mypassword=$_POST['mypassword'];

}
else{

    returnBack();
}
if(isset($_POST['myemail']))  {

    $myemail=$_POST['myemail'];
}
else{

    returnBack();
}
if(isset($_POST['myname']))  {

    $myname=$_POST['myname'];
}
else{

    returnBack();
}
if(isset($_POST['mylastname'])){

    $mylastname=$_POST['mylastname'];

}
else{

    returnBack();
}
/////////////////////////////////////////////////////////////*******CONNECT TO SERVER ******************************************************************/
try {
  # MySQL with PDO_MYSQL
  $DBH = new PDO("mysql:host=$hostname;dbname=$database", $username, $password);
  $DBH->setAttribute( PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION );

}
catch(PDOException $e) {
    echo "I'm sorry, I'm afraid I can't do that.";
    file_put_contents('PDOErrors.txt', $e->getMessage(), FILE_APPEND);
}
////////////////////////////////////////////////////////////***********INSERT REGISTER DATA INTO DB ***************************************************************/
//$encrypt_password = md5($mypassword);

$insertdata = $DBH->prepare("INSERT INTO members (username, password, email, firstname, lastname ) VALUES ('$myusername','$mypassword','$myemail','$myname','$mylastname')");
$insertdata->execute();
echo "success";

$DBH = null;

<table width="300" border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="#CCCCCC">
<tr>
<form name="register" method="post" action="insertnewmem.php">
<td>
<table width="100%" border="0" cellpadding="3" cellspacing="1" bgcolor="#FFFFFF">
<tr>
<td colspan="3"><strong>Registration Form </strong></td>
</tr>
<tr>
<td width="78">Username</td>
<td width="6">:</td>
<td width="294"><input name="myusername" type="text" id="myusername" ></td>
</tr>
<tr>
<td>Password</td>
<td>:</td>
<td><input name="mypassword" type="text" id="mypassword"></td>
</tr>
<tr>
<td>Email</td>
<td>:</td>
<td><input name="myemail" type="text" id="myemail"></td>
</tr>
<tr>
<td>First Name</td>
<td>:</td>
<td><input name="myname" type="text" id="myname"></td>
</tr>
<tr>
<td>Last Name</td>
<td>:</td>
<td><input name="mylastname" type="text" id="mylastname"></td>
</tr>
<tr>
<td>&nbsp;</td>
<td>&nbsp;</td>
<td><input type="submit" name="Submit" value="Register"></td>
</tr>
</table>
</td>
</form>
</tr>
</table>

if(isset($_POST['variable']) && $_POST['variable'] !== "")